1. Field of the Invention
This invention relates to a fluorescent material which is produced after a solid solution comprising gallium nitride and indium nitride have been doped with a doping substance, or to a fluorescent material which emits light by electron beam excitation, has a property to emit light different in color according to what materials are chosen for the constituents, and has an excellently long life.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 51-41686 discloses a fluorescent material which is produced after Ga.sub.2 O.sub.3 has been nitrified in an atmosphere of ammonia to produce GaN, and then GaN, being made as a substrate, has been doped with Cd a dopant. This fluorescent material is not applied, however, for the purpose of light emission by electron beam excitation, and the said reference does not give any mention of the method how to use the fluorescent material to emit light by electron beam excitation.
When Ga.sub.2 O.sub.3 is nitrified in an atmosphere of nitrogen, nitrification of Ga.sub.2 O.sub.3 starts from the surface. When the system is heated to a high temperature, the nitrified surface is oxidized again. Namely, gallium nitride has a tendency to easily lose nitrogen. This is the reason why Ga.sub.2 O.sub.3 becomes an n type, has a very low resistance and emits light even when not doped.
Emission of light from gallium nitride occurs as a result of the pairing between donors (D) and acceptors (A). Acceptors are formed after Zn, Mg, etc. are added. Donors are nitrogen deficits naturally produced. When a conventional procedure is used for increasing the concentration of donors, it results in the increase of nitrogen deficits of the material, which will degrade the crystal regularity of the material. As seen from this, with gallium nitride produced by a conventional procedure, it is impossible to adjust the number of donors to a desired value.
Further, gallium nitride has a possibility of being oxidized in the presence of oxygen. Accordingly, if Ga.sub.2 O.sub.3 or an oxide is used as a starting material, it is quite difficult to convert it completely into a nitride compound. Even if this is feasible, the resulting gallium nitride will be inferior in quality because residual oxygen therein will have an adverse effect on light emission.